1. Field of the Invention
The present invention relates to a method of constructing a shell for a room air conditioner/heat pump that has good lateral strength and, more particularly, to the method of punching holes at each corner so that a screw inserted in the punched hole passes through the outermost sheet metal only to readably engage the innermost sheet metal at each corner, which screw provides lateral strength to the shell.
2. Description of the Prior Art
Housings for room air conditioners/heat pumps have been inserted inside of windows or openings in buildings for some time. Thereafter, the room air conditioner/heat pump would be positioned in the housing. In the past, a housing that encloses the air conditioner/heat pump except on each end would be used with vents or louvers as needed to allow air to pass there through. As time passed, and manufacturing capabilities increased, the housing became a shell that was formed from stamped sheet metal with open ends. The sheet metal would be stamped to a predetermined size and configuration complete with holes, louvers and notches therein.
The stamped sheet metal would then be formed to the desired shape to make a shell, which shell was held together by clinching. The shell may be either a full rectangular box with open ends or a U-shaped rectangular box with open ends and a shell brace across one open end. The shell would then be mounted in a window or an opening in the wall. Afterwards, the air conditioner/heat pump would be inserted in the shell.
The typical way the shell would be held together would be by clinching or by welding. However, a clinched shell has very little lateral strength. If any force is exerted laterally on the sides of the shell, the clenched corners have a tendency to break. If the breakage occurs during shipment, the shell would have to be replaced by the manufacturer. The replacing of the shells is very expensive.
One option to give lateral strength to the shell would be to insert screws in each corner of the shell. However, this would require screw holes to be formed in the shell at the time of stamping and after folding for the screw holes to line up. Normally, because of tolerances in the folding of the sheet metal, the screw holes do not line up. Further, if the screw is threaded into two pieces of sheet metal, there is a tendency for space to form between the two pieces of sheet metal, thereby decreasing the strength of the screw connection.
The reason for the space is because the screw will not threadably engage both pieces of sheet metal at the same time. Threadably engaging a first piece of sheet metal tends to draw the first piece along the screw and away from the second piece of sheet metal.
In the prior art, there are many different examples of screws joining two pieces of sheet metal, such as shown in U.S. Pat. No. 3,156,152 to Reed. However, as can be seen in FIG. 4 of Reed, the thread 20 threadably connects to both superimposed metal sheets 30 and 32. This has a tendency to form space between the metal sheets 30 and 32, which decreases the strength of the connection. Many times in the past, the screw would be threadably connected to both pieces of overlapping sheet metal with the result being that someone would have to forcibly attempt to draw the two pieces of sheet metal together.
An example of a way to form an appliance housing is shown in U.S. Pat. No. 2,897,035 to Dorsey. As can be seen in the figures, preformed socket 32 has to align with knob 17 having a center 28 therein. Thereafter, sheet metal screw 33 has to self-tap into multiple layers of sheet metal.
None of the prior art shows two overlapping pieces of sheet metal that form a housing, and after being formed, is punched with the outermost sheet metal receiving a screw there through without a threadable connection, but threadably connecting to an innermost sheet metal to draw the two pieces of sheet metal together. Such a connection is not shown in the prior art.